1. Field of the Invention
The present invention relates generally to a molding machine and, more particularly, to an improvement of a base frame for supporting a stationary platen and a movable platen each carrying a mold in the molding machine.
2. Description of the Related Art
In a clamping mechanism of a molding machine (e.g., an injection molding machine), it is generally required that, when the molds are to be opened or closed by the travel of a movable platen relative to a stationary platen (i.e., a mold clamping or opening operation), a movable mold attached to the movable platen is accurately moved, in translation or parallel displacement, relative to a stationary mold attached to the stationary platen. In other words, it is necessary to move the movable platen while maintaining a predetermined parallelism (or a parallel positional correlation) between the stationary mold and the movable mold. If the parallelism is disturbed, the smoothness of the opening/closing motion of the molds may be deteriorated, molding defects may be caused due to an inaccurate clamping, or the molds may be damaged due to an irregular clamping pressure.
Conventionally, in order to accurately move, in translation or parallel displacement, the movable mold relative to the stationary mold, it is known that a platen support formed from a motion facilitating element, such as a slide plate, a roller or a linear guide, is attached to the bottom of the movable platen and is placed in a movable manner on the supporting surface of a base frame of the molding machine, so that the weight of the movable platen is borne on the base frame while the movable platen is moved along the support surface of the base frame. For example, Japanese Unexamined Patent Publication (Kokai) No. 9-262884 (JP9-262884A) discloses an injection molding machine in which a pair of linear guide units (i.e., platen supports), provided on a base frame, guide and support a movable platen on the base frame. Also, Japanese Unexamined Patent Publication (Kokai) No. 9-225979 (JP9-225979A) discloses an injection molding machine, in which first and second linear guide mechanisms (i.e., platen supports) possessing jointly a pair of guide rails provided on a base frame, guide and support a stationary platen and a movable platen, respectively, in a movable manner on the base frame.
Also, Japanese Patent Publication No. 2696706 (JP2696706B2) discloses a clamping mechanism of an injection molding machine, in which a slide mechanism (i.e., a platen support), composed of a guide channel provided on a base frame and a rib provided on the bottom face of the movable platen, guide and support the movable platen on the base frame. Also, Japanese Examined Utility Model Publication (Kokoku) No. 6-39960 (JP6-39960Y2) discloses a clamping mechanism of a molding machine, in which a tie bar tying a stationary platen to a rear platen guides and supports a movable platen, while a support unit (i.e., a platen support) slidable or rollable on the supporting surface of a base frame is attached to the bottom of the movable platen in such a manner as to be shiftable relative to the movable platen by a predetermined distance in a height direction, so that the support unit supports the weight of the movable platen in an auxiliary manner.
Also, Japanese Unexamined Patent Publication (Kokai) No. 2000-280275 (JP2000-280275A) discloses an injection molding machine including an intermediate mold arranged between a stationary mold and a movable mold, in which a slide guide is provided, as means similar to a platen support, on a tie bar for preventing the intermediate mold cantilevered on a stationary platen or a movable platen from being lowered due to its own weight.
The base frame of the molding machine is liable to be bent due to its own weight as well as the weight of components mounted on the base frame, such as a movable mold, a stationary mold, a rear platen, and so on. The bending or flexure generated in the base frame may affect the parallelism between the stationary mold and the movable mold, i.e., the parallelism between the stationary platen and the movable platen, even when the above-described platen support is used. In other words, the parallelism between the stationary platen and the movable platen depends on the rigidity or stiffness of the base frame. However, if the rigidity of the base frame is increased to such a degree that the parallelism between the stationary platen and the movable platen can be maintained in a high accuracy, the production cost of the molding machine may, as a result, rise.
As a solution for ensuring the rigidity of a base frame in the molding machine, Japanese Unexamined Patent Publication (Kokai) No. 7-323453 (JP7-323453A) discloses a clamping mechanism of a molding machine, in which a set plate having a desired rigidity is supported on the top plate of a base frame in a three-point or four-point suspension system, and a movable platen and a rear platen are secured on the set plate. The rigidity of the set plate is selected as such a degree that any influence of the weight of the clamping mechanism over the parallelism between the stationary platen and the rear platen can be eliminated. In this arrangement, the base frame may still be bent due to the weight of the set plate and components supported thereon, so that it is difficult to stably ensure the accuracy of the translation or parallel displacement of the movable platen.